Second MRI for offensive lineman who has missed most of camp

Chargers at 49ers

As Jared Gaither’s recovery continues at a crawl, the Chargers have accepted they may be without their starting left tackle to start the season.

They are monitoring their options.

On Tuesday, Gaither was officially ruled out for Thursday’s exhibition game against the 49ers. He wasn’t at practice, instead undergoing an MRI, coach Norv Turner said.

It’s the second MRI for Gaither since he suffered back spasms July 28 in the team’s weight room. He hasn’t practiced since, missing about all of training camp and, soon, the entire preseason.

Why Gaither had the latest MRI is unclear. The team gave no indication of a recent setback.

After sustaining the injury, the 6-foot-9, 335-pound lineman was given weeks of rest. Tuesday’s scan came exactly one week after he increased his activity, rehabbing on the side field at the start of Chargers practices.

Regardless, Gaither’s slow recovery has the team concerned about his status for its Sept. 10 regular-season opener at Oakland.

Even if he was to begin practicing next week, there is a question of whether he’d be ready to face the Raiders in such short turnaround.

“Our plan is to get him ready to play as soon as he can be ready to play,” Turner said. “We’re working hard to get that done. Right now, he’s not ready to play. ... If he doesn’t practice, it’s going to be hard to play in the opener.”

The backup options in place begin with rookie Michael Harris.

The Chargers have been grooming the undrafted tackle, who’s taken first-team reps the past month and started every exhibition game in Gaither’s place.

Of the team’s veteran tackles, Mario Henderson is not expected to make the team, and Anthony Davis is not a roster lock, either.

That leaves Tyronne Green as a potential No. 2 reserve option. If needed, he can move to tackle from starting left guard, a scenario in which guard-center Rex Hadnot, who has 93 starts in 113 career games, would take Green’s place.

The Chargers are also scrutinizing the tackles, as well as defensive backs, that are released during this week’s league-wide cuts.

On Monday afternoon, the NFL reduced every team’s maximum roster size from 90 to 75 players. By 6 p.m. Friday, teams must be down to 53.

Gaither signed a four-year, $24.5 million contract in March with an $8 million signing bonus and $13.5 million guaranteed. He first joined the Chargers late last season, helping solidify their offensive line and keying a four-win stretch over the final five games.

Without Gaither, the Chargers allowed 28 sacks in 11 games, ranking 23rd in the league in fewest sacks allowed.

With Gaither, they ceded two sacks in five games, first over that period.